Programmable inductors are essential components in Radio Frequency (RF) circuits in the domains of telecommunications, mobile communications, wireless local area networks (WLAN), TV, networking and so on. With such devices, many useful applications may be implemented, such as programmable voltage controlled oscillators (VCO), programmable filters, output buffers using a programmable over-shoot or boost, programmable features, i.e., gain, linearity, matching networks, in circuits like LNAs (Low Noise Amplifiers), mixers, power amplifiers and the like.
A traditional programmable inductor includes many inductors and switches in order to achieve the programmability function. For example, referring to FIG. 1, a schematic diagram illustrates a conventional programmable inductor implementation using multi-inductors technique with switches.
In particular, an exemplary programmable inductor 100 is shown having two conductors 102 and 104 and two switches 106 and 108. When the switches 106 and 108 are both connected, the inductors 102 and 104 are connected to the inductor terminals in parallel. When either of the switches 106 and 108 have been disconnected, only inductor 102 is connected to the inductor terminals. Therefore, with the control of the switches 106 and 108, inductors 102 and 104 may be connected to the inductor terminals in different configurations. Consequently, two different inductor values may be obtained in the inductor terminals, and the inductance value of this inductor is programmable.
However, this type of programmable inductor presents a number of limitations. The programmable inductor 100 takes too much area space because the inductor number increases with the number of programmable values. Therefore, when an area of an inductor is limited, the programmable values range are also limited. Furthermore, because of the large area, an inductor's radiations and magnetic coupling with other blocks or devices also increase, causing further performance degradations.
For example, to address the above drawbacks, various solutions have been advanced. One solution presented in, namely, US Patent Application 2006/0033602 A1, proposes a variable integrated inductor which has an inductance value that may be switched between two or more values. This reference proposes a principle based on the coupling between a primary inductor and a secondary one, the last being programmable with switches, which makes the coupling itself variable and as a result, the value of the primary inductor also varies.
However, in this type of variable integrated inductor, in one scenario where many secondary inductor pairs are disposed in a plan with each one placed near one another, the inconvenience of spatial extension and increasing coupling and radiation issues are present. In another scenario where these secondary inductor pairs are superposed over each other, there is no area issue which can be invoked. Further, another limitation arises resulting from the parasitic capacitors between the secondary inductors and the substrate on a side, and the primary inductor and the secondary inductors on the other side. These parasitic capacitors define the own resonance frequency of the primary and secondary inductors. The higher the capacitors are, the lower are the resonance frequencies, and an inductor may not be used at a frequency close or inferior to its resonance frequency. Therefore, there is a limitation on the frequency of use, resulting primarily from the superposition of many inductors, which may affect either the primary or the secondary inductors. Consequently, the increase of the programmability range may not be implemented without giving an upward limitation on the utilization frequency of a given programmable inductor.
Therefore, in view of these concerns, there is a continuing need for developing a new and improved programmable integrated inductor which would avoid the disadvantages and above mentioned problems while being cost effective and simple to implement.